console.log(typeof 1);//number
console.log(typeof 1.1);//number
console.log(typeof 1n);//bigint
console.log(typeof "abc");//STRING
console.log(typeof 'abc');//STRING
console.log(typeof `abc`);//STRING
console.log(typeof false);//boolean
console.log(typeof true);//boolean
console.log(typeof undefined);//undefined 常量的数据类型都是undefined
var  a;
console.log(typeof a);//如果变量声明不复制 默认等于undefined
var  a=Symbol("name")
console.log(typeof a)//symbol 主要用于创建私有属性
var c=null
console.log(typeof c);//object